1. Field of the Invention
This invention relates generally to reciprocating piston type internal combustion (I.C.) engines for motor vehicles. More specifically it relates to I.C. engines having variable compression ratio connecting rods, especially to systems, mechanisms, and strategies that use hydraulic fluid for accomplishing connecting rod length change while an engine is running.
2. Background Information
The compression ratio built into the design of an internal combustion engine that has a non-variable compression ratio must be selected to avoid objectionable engine knock that would otherwise occur during certain conditions of engine operation if the compression ratio were higher. However, those conditions that give rise to engine knocking in a motor vehicle typically prevail only for limited times as the vehicle is being driven. At other times, such as when it is lightly loaded, the engine could operate with better efficiency, and still without knocking, if the compression ratio could be made higher.
Certain of those commonly owned pending patent applications incorporated herein by reference disclose engine connecting rods whose lengths can be changed automatically to change engine compression ratio. When the connecting rods have longer effective lengths, the engine has a higher compression ratio. When the connecting rods have shorter effective lengths, the engine has a lower compression ratio.
Included with the disclosures of those patent applications are hydraulic systems for effecting connecting rod length changes. Those systems use engine motor oil as hydraulic fluid. Change in overall effective length may be accomplished in either the connecting rod, or the piston, or in both, but it is preferred that effective length be changed at the large end of the connecting rod so that the incorporation of variable compression ratio by connecting rod length change does not adversely contribute to the reciprocating mass of an engine.
A connecting rod disclosed in the referenced applications comprises an assembly that contains a first part, a second part, and a third part assembled together to form the large end of the connecting rod assembly and provide a variable length for the connecting rod assembly. The first part is a semi-circular cap. One of the second and third parts is fastened tight to the first part. Guides disposed at opposite sides of the large end operatively relate the other of the second and third parts and the fastened parts to provide for relative sliding motion between the other of the second and third parts and the fastened parts over a limited adjustment range to change the length of the connecting rod assembly. Each connecting rod employs two such locking mechanisms, a first for locking the connecting rod in one length and a second for locking the connecting rod in another length.
When length is to be changed, a hydraulic system that uses engine motor oil as hydraulic fluid unlocks whichever one of the locking mechanism is locked. With both locking mechanisms unlocked, the centerline of the connecting rod large end is free to move relative to the centerline of the crank pin on which it is mounted via a bearing retainer, such as between a position of concentricity and a position of eccentricity. Inertial force acts to move the connecting rod such that the centerline of the large end is re-positioned relative to the centerline of the crank pin, thereby changing the effective length of the connecting rod from one length to the other. Upon completion of the length change, the other locking mechanism locks the connecting rod in the new length.
Requirements for any particular hydraulic system depend on the nature of the locking mechanisms. For certain types of locking mechanisms, a hydraulic system for effecting connecting rod length change from an initial length to a new length uses an increase in hydraulic pressure to cause the length change, but also requires maintenance of increased hydraulic pressure to maintain the new length. Discontinuance of the increased hydraulic pressure causes the connecting rod to revert to its original length.
For other types of locking mechanisms, another type of hydraulic system for effecting connecting rod length change from an initial length to a new length uses an increase in hydraulic pressure to cause the length change, but does not require maintenance of increased hydraulic pressure to maintain the new length. This is because of the particular types of locking mechanisms and because hydraulic pressure for unlocking each mechanism is delivered to each respective mechanism via its own devoted passageway when the respective mechanism is to be unlocked.
Each type of hydraulic system possesses its own particular advantages. The present invention concerns further improvements in such systems.
The present invention relates to novel systems, mechanisms, and strategies: for operating connecting rods, especially connecting rods of the types disclosed in the commonly owned referenced patent applications, to different lengths while an engine is running, thereby changing the engine compression ratio.
One generic aspect of the invention relates to an internal combustion engine comprising cylinders within which combustion takes place and an engine mechanism comprising a crankshaft that rotates about a crank axis and connecting rods via which the crankshaft is operatively coupled with pistons that reciprocate within the cylinders. An oiling system delivers oil under nominal engine lubrication pressure to lubricate moving surfaces of the engine mechanism and comprises first and second control passages to effect engine compression ratio change. Selectively operated hydraulic control devices cause pressure in the first passage to be greater than pressure in the second passage to effect an increase in engine compression ratio and cause pressure in the second passage to be greater than pressure in the first passage to effect a decrease in engine compression ratio.
Another generic aspect of the invention relates to a method of changing compression ratio of an internal combustion engine having cylinders within which combustion takes place, an engine mechanism comprising a crankshaft that rotates about a crank axis and connecting rods via which the crankshaft is operatively coupled with pistons that reciprocate within the cylinders, and an oiling system for delivering oil under nominal engine lubrication pressure to lubricate moving surfaces of the engine mechanism and comprising first and second control passages to effect engine compression ratio change. The method comprises selectively operating hydraulic control devices for causing pressure in the first passage to be greater than pressure in the second passage to effect an increase in engine compression ratio and for causing pressure in the second passage to be greater than pressure in the first passage to effect a decrease in engine compression ratio.
Further aspects will be seen in various features of presently preferred embodiments of the invention that will be described in detail.